An image forming method using an inkjet recording method is a method for forming an image by discharging an ink supplied from an ink tank through a channel from a recording head for discharge. The inkjet recording method can form an image simply and inexpensively and therefore has been used for forming various images. As one of the inks for use in the inkjet recording method, there is an actinic radiation-curable inkjet ink. The actinic radiation-curable inkjet ink comprises a photocurable compound, and therefore an ink component can be cured by polymerizing the photocurable compound through irradiation with actinic radiation such as ultraviolet rays. When an image is formed using the actinic radiation-curable inkjet ink, it is easier to immobilize a discharged ink and an image with little bleeding can be formed on various recording media than when a solvent-based ink composition is used.
For example, a gel ink comprising a gelling agent such as wax is developed in order to improve a pinning property of the actinic radiation-curable inkjet ink. In a recording method using such an ink, an image is formed by melting gel at high temperatures to land an ink droplet on a recording medium, and then allowing the landed ink droplet to undergo gelation (solidify). There have been some cases where ink dots are isolated and an irregularity occurs in an image portion or nonuniform feeling in glossiness is brought about when the landed ink droplet solidifies rapidly. For example, in PTL 1, the farther a recording medium (normal paper or the like) is apart from heating means installed on an upstream side, the lower the temperature of the recording medium is, and therefore the gelation temperature of an ink to be discharged on a downstream side is made to lower according to the temperature of the recording medium, thereby preventing the rapid solidification of the ink on the downstream side and stabilizing the glossiness.
In addition, PTL 2 discloses an ink set in which the gelation temperature of a clear ink is made higher than the gelation temperature of a color ink as an ink set for forming a printed image having a high image quality and a uniform matted feeling. In this literature, the relationship among the gelation temperatures of a plurality of color inks to be used is not described, but, with respect to the gelation temperatures of color inks to be printed in the order of Y, M, C, and K in a color ink set used in Examples, the gelation temperature of K to be printed finally is set to be lower than the gelation temperature of Y to be printed first.
In PTL 1 and PTL 2 described above, the specific description on the formation of an image using thick paper or corrugated paper as a recording medium is not made. With respect to an inkjet recording method intended for use for thick paper, corrugated paper, or the like, for example, PTL 3 discloses a method and an apparatus for forming an image on corrugated paper using an ultraviolet ray-curable gel ink.